JP2017056725A - Thermosensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermosensitive recording medium which is excellent in thermal discoloration resistance, especially thermal discoloration resistance of a blank part and further has improved surface strength.SOLUTION: The thermosensitive recording medium includes: a support; an undercoat layer which is provided thereon, contains a pigment and a binder as main components, and further contains cationic substances; and a thermosensitive recording layer which is provided further thereon and contains a colorless or light-colored electron-donating leuco dye and an electron-accepting developer as main components. The pigment contained in the undercoat layer is rosette-type precipitated calcium carbonate which is obtained by radially aggregating primary particles having a spindle shape to form secondary particles and which has a bulk density of 240 g/L or less. Furthermore, the undercoat layer contains, as the cationic substances, a cationic sizing agent, a cationized starch, a water-soluble metal salt, and the like.SELECTED DRAWING: None

Description

  The present invention utilizes a coloring reaction between a colorless or light-colored electron-donating leuco dye (hereinafter also referred to as “leuco dye”) and an electron-accepting developer (hereinafter also referred to as “developer”). The present invention relates to a heat-sensitive recording material which is excellent in heat discoloration resistance, particularly heat resistance discoloration property of a blank paper portion, and has improved surface strength.

In general, a thermal recording material is usually a colorless or light leuco dye and a developer such as a phenolic compound, each of which is ground and dispersed into fine particles, and then mixed together to form a binder, a filler, a sensitivity improver, A coating liquid obtained by adding a lubricant and other auxiliary agents is coated on a support such as paper, synthetic paper, film, plastic, etc., and is widely used as various recording media.
In recent years, such heat-sensitive recording materials have been used in facsimiles, computer terminal printers, automatic ticket vending machines, measurement recorders, and the like. Furthermore, the use of thermal recording media has been expanded to various tickets, receipts, labels, bank ATMs, gas and electric meter readings, and car tickets, etc. There is a need to preserve the image area and the blank paper area under such conditions as, for example, an environment such as a high temperature in a car in midsummer. In order to solve such a problem, configurations of a developer, a dye, and a protective layer have been studied (Patent Documents 1 to 3, etc.).
It has also been proposed to improve the recording sensitivity and printing runnability by providing an undercoat layer containing an inorganic pigment or plastic particles between the support and the heat-sensitive recording layer (Patent Documents 4, 5, etc.).

JP-A-10-86529 JP2008-6739 JP 2010-94986 JP 05-162446 A JP2012-076228

Conventionally, in order to improve the heat discoloration resistance of the thermal recording material, particularly the heat discoloration resistance of the white paper portion, the constitution of the developer, the dye and the protective layer has been mainly studied as described above (Patent Literature). 1 to 3), the present inventors have studied to improve the heat discoloration of the thermal recording medium by providing an undercoat layer between the support and the thermosensitive recording layer, and the constitution of the undercoat layer. An undercoat layer is provided between the support of the recording medium and the heat-sensitive recording layer. Spindle-shaped primary particles as a pigment aggregate radially to form secondary particles in the undercoat layer, thereby having a characteristic Rosetta-type shape. It has been found that by containing light calcium carbonate and limiting the bulk density to a specific bulk density, the heat discoloration resistance of the thermal recording material, particularly the heat discoloration resistance of the blank paper portion, is improved (International Publication WO2015 / 141497). ).
Rosetta-type light calcium carbonate used in the present invention has a specific shape and bulk density, and an undercoat layer containing such a pigment effectively transfers heat from the support side to the thermosensitive recording layer. Therefore, it is considered that heat transfer to the thermosensitive recording layer is reduced even when stored in a high temperature environment, and heat discoloration is excellent (see Reference Example 1 (Table 1) for Reference Examples 2 and 3 described later). I want to be.)
Further, when the undercoat layer contains such a pigment, it is considered that the absorption performance peculiar to the material contained in the undercoat layer or the adjacent thermosensitive recording layer is exhibited. For example, after the coloring material contained in the heat-sensitive recording layer, particularly the developer, is melted by heating with a thermal head at the time of printing, it cannot participate in color development, i.e., there is no opportunity for chemical reaction with the leuco dye, resulting in surplus. It is considered that the developer was absorbed by the undercoat layer. As a result, it is considered that the thermal head is less likely to become scum and the printing running property (head scum resistance) is improved. Moreover, it is thought that it also affects the expression of the binder contained in such an undercoat layer (refer to Reference Example 1 (Table 1) for Reference Examples 2 and 3 described later).
The present inventors have found that the surface strength of the heat-sensitive recording material is further improved by adding a cationic substance to such an undercoat layer.

According to the study by the present inventors, pigment particles by electrostatic interaction can be obtained by further adding a cationic substance to the undercoat layer of the heat-sensitive recording material (International Publication WO2015 / 141497) already completed as described above. It is considered that the surface strength of the heat-sensitive recording material is further improved by the formation of the agglomerates and the relaxation of the pigment in the undercoat layer or on the support.
That is, the present invention includes a support, an undercoat layer containing a pigment and a binder as main components provided on the support, and further containing a cationic substance, and a colorless layer provided on the undercoat layer. Or a heat-sensitive recording layer comprising a light-colored electron-donating leuco dye and an electron-accepting developer as main components, wherein the pigment contained in the undercoat layer comprises spindle-shaped primary particles. It is a rosette-type light calcium carbonate formed by agglomerating radially to form secondary particles, and has a bulk density of 240 g / L or less.

The heat-sensitive recording material of the present invention comprises a support, an undercoat layer provided on the support, and a heat-sensitive recording layer provided on the undercoat layer.
This undercoat layer contains a pigment and a binder as main components, and this pigment is rosetta-type light calcium carbonate formed by agglomerating spindle-shaped primary particles radially to form secondary particles.
The bulk density of the rosetta type light calcium carbonate is 240 g / L or less, preferably 150 to 220 g / L. This bulk density is measured in accordance with JIS-K-5101-12-1 (pigment test method-part 12: apparent density or apparent specific volume-section 1: stationary method).

Rosetta-type light calcium carbonate used in the present invention is formed by agglomerating primary particles of spindle-shaped light calcium carbonate in a radial manner to form secondary particles. From the vicinity of the center, the primary particles are radially extended in the longitudinal direction.
Rosetta-type light calcium carbonate used in the present invention is, for example, Specialty Minerals Inc. It is available as Albuquer LO (bulk density: 210 g / L) manufactured by KK or TP221BM (bulk density 230 g / L) manufactured by Okutama Kogyo Co., Ltd.
Rosetta-type light calcium carbonate may be used after being pulverized by a known pulverizer such as a ball mill, an attritor, or a sand glider.

In the undercoat layer of the present invention, a pigment other than the rosetta-type light calcium carbonate of the present invention may be used. Examples of pigments other than rosetta-type light calcium carbonate include light calcium carbonate formed by forming irregularly shaped secondary particles, and light brown chestnut light formed by agglomerating needle-like primary particles radially to form secondary particles Calcium carbonate, light calcium carbonate, heavy calcium carbonate, primary calcium, spindle, columnar, square, spherical, etc., without forming secondary particles, (calcined) kaolin, clay, talc, silica , Aluminum oxide, zinc oxide, titanium oxide, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, aluminum silicate, magnesium silicate, calcium silicate and the like. These pigments can be used alone or in admixture of two or more.
When the undercoat layer contains a pigment other than the rosetta type light calcium carbonate of the present invention, the content of the rosetta type light calcium carbonate of the present invention is the same as the total pigment contained in the undercoat layer (the rosetta type light calcium carbonate of the present invention). Inclusive) is preferably 50% by weight or more, more preferably 70% by weight or more, particularly preferably 90% by weight or more.

The undercoat layer of the present invention further contains a cationic substance. The cationic substance in the present invention is a substance that exhibits a cationic property when dissolved or dispersed in water.
It is considered that when the undercoat layer of the present invention further contains a cationic substance, electrostatic interaction is strong and pigment aggregates are easily formed.
Examples of the cationic substance include a cationic sizing agent, cationized starch, water-soluble metal salt, epichlorohydrin resin, and cationic polyacrylamide.
In the present invention, the cationic substance is preferably at least one selected from the group consisting of a cationic sizing agent, a cationized starch, and a water-soluble metal salt, and more preferably a cationic sizing agent.
In the case where the cationic substance is at least one selected from the group consisting of a cationic sizing agent, a cationized starch, and a water-soluble metal salt, since the electrostatic interaction is more strongly expressed, the above effect can be achieved with other cationic substances. This is likely to be more prominent than when substances are used. Furthermore, HCO cationic substance is dissolved from the rosette type precipitated calcium carbonate in the undercoat layer ₃ ^- or CO 3 ^_2-, or -OH derived from a polyvinyl alcohol binder ^- react with anions such as, primed with time Since the layer is hydrophobized, it is considered less susceptible to the effects of humidification and heating, and reprintability (coloring sensitivity after storage) is improved.

  Examples of the cationic sizing agent include a styrene sizing agent, an acrylic sizing agent, and a styrene acrylate sizing agent, and a styrene sizing agent or a styrene acrylate sizing agent is preferable. These may be used alone or in combination. Specific examples of this cationic sizing agent include Polymeron 360 (styrene sizing agent) (manufactured by Arakawa Chemical Industries), SE2250 (emulsion styrene acrylate sizing agent), SS2753 (solution type styrene acrylate sizing agent) (above , Produced by Seiko PMC Co., Ltd.).

  This cationized starch is obtained by cationizing starch, and a method using an ammonium salt or amine salt such as a quaternary ammonium compound having a glycidyl group as a cationizing agent is known for cationization of starch. Specific examples of the cationized starch include amylofax T2600, amylofax 00 (above, manufactured by Abebe Japan), neotack # 20T, neotack # 30T, neotuck # 40T (above, manufactured by Nippon Food Chemical Co., Ltd.), Ace Din HP -100, Ace Din HP-150, Ace Din HP-SP20 (manufactured by Daiwa Chemical Industry Co., Ltd.) and the like. These may be used alone or in combination.

  As this water-soluble metal salt, calcium chloride, calcium nitrate, calcium lactate, aluminum chloride, aluminum nitrate, aluminum sulfate, aluminum lactate, magnesium chloride, magnesium nitrate, magnesium sulfate, magnesium lactate, etc. can be used, preferably magnesium sulfate Alternatively, aluminum sulfate is used. These may be used alone or in combination.

  Examples of the epichlorohydrin resin include a polyamide epichlorohydrin resin and a polyamine epichlorohydrin resin, and a polyamide epichlorohydrin resin or a polyamine epichlorohydrin resin is preferable. These may be used alone or in combination. Moreover, as an amine which exists in the principal chain of an epichlorohydrin-type resin, the thing from a primary to a quaternary can be used, and there is no restriction | limiting in particular. Specific examples of this epichlorohydrin resin include Sumire Resin 650 (30), Sumire Resin 675A, Sumire Resin 6615 (manufactured by Sumitomo Chemical Co., Ltd.), WS4002, WS4010, WS4011, WS4020, WS4024, WS4030. , WS4046, WS4010, CP8970 (manufactured by Seiko PMC Co.).

Examples of polyacrylamide include anionic polyacrylamide, nonionic polyacrylamide, and cationic polyacrylamide, and it is preferable to use cationic polyacrylamide that exhibits strong electrostatic interaction.
The cationic polyacrylamide of the present invention mainly has a cationic group in the polymer. As described above, the cationic polyacrylamide has an anionic group in the polymer as long as it exhibits a cationic property when dissolved or dispersed in water. Also good.
The molecular weight of the cationic polyacrylamide is not particularly limited, but in the present invention, it is preferable to use a cationic polyacrylamide having a molecular weight of about 100,000 to 6,000,000 because the electrostatic interaction is appropriately expressed.
Specific examples of the cationic polyacrylamide used in the present invention include DH4162, DH4196, HG5324 (manufactured by Seiko PMC), Harifix UF-570 (manufactured by Harima Kasei). These may be used alone or in combination.

Further, the undercoat layer of the present invention may further contain organic hollow particles. When organic hollow particles are contained in the undercoat layer, the heat discoloration property of the blank paper portion is further improved, the heat insulation property of the undercoat layer is improved, and a thermosensitive recording material excellent in color development sensitivity can be obtained.
These organic hollow particles are micro hollow particles that are made of a thermoplastic resin as a shell and contain air or other gas inside, and are already in a foamed state.
Examples of the thermoplastic resin include polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic acid ester, polyacrylonitrile, polybutadiene, and copolymers thereof. In particular, styrene resins such as polystyrene, acrylic resins such as polyacrylic acid esters and polyacrylonitrile, copolymers thereof, or copolymer resins mainly composed of polyvinylidene chloride and polyacrylonitrile are preferable. Specifically, such organic hollow particles are available under the trade name SX8782 manufactured by JSR Corporation, trade names MH5055 and MH8103K manufactured by Nippon Zeon Co., Ltd., and trade name Ropeke HP-91 manufactured by Rohm & Haas Japan.

The hollow ratio of the organic hollow particles is preferably 40 to 90%, more preferably 45 to 90%. When the hollow ratio is less than 40%, the heat insulation becomes insufficient, and heat energy from the thermal head or the like is easily released out of the heat-sensitive recording medium through the support. A sufficient effect may not be obtained.
Here, the hollow ratio is calculated from the outer diameter and inner diameter of the hollow particles, and is represented by the hollow ratio = (the inner diameter of the hollow particles / the outer diameter of the hollow particles) ³ × 100 (%).

The average particle diameter of the organic hollow particles is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. When the average particle size is larger than 10 μm, the smoothness of the surface of the heat-sensitive recording layer formed on the undercoat layer is lowered, and the adhesion between the heat-sensitive recording material and the thermal head is lowered, so that a sufficient effect cannot be obtained. There is. On the other hand, when the average particle size is smaller than 0.5 μm, the amount of the gas contained in the hollow particles is small, and thus a sufficient effect may not be obtained.
Here, the average particle diameter is indicated by a median diameter d _{50 in} which the particles on the large side and the small side are equivalent (volume basis) when the particles are divided into two according to the diameter. It can be measured by the device.

As a binder used in the undercoat layer, polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, and terminal alkyl-modified polyvinyl alcohol, hydroxyethyl cellulose, Cellulose ethers and derivatives thereof such as methylcellulose, ethylcellulose, carboxymethylcellulose, acetylcellulose, starch, enzyme-modified starch, thermochemically modified starch, oxidized starch, esterified starch, starch such as etherified starch (eg, hydroxyethylated starch) Water-soluble trees such as polyacrylamide, polyacrylamide, anionic polyacrylamide, and amphoteric polyacrylamide ; Urethane resins such as polyester polyurethane resin, polyether polyurethane resin, polyurethane ionomer resin, styrene such as styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-butadiene-acrylic copolymer Acrylic resin consisting of monomer components copolymerizable with (meth) acrylic acid such as butadiene resin, (meth) acrylic acid and (meth) acrylonitrile, olefins such as ethylene, propylene and butylene, and (meth) Polyolefin resin consisting of monomer components that can be copolymerized with olefins such as unsaturated carboxylic acids such as acrylic acid, maleic acid, itaconic acid, fumaric acid, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, poly Vinyl chloride, polyvinyl chloride Emissions, polyacrylic acid esters, Porisuchirosu and their copolymers, silicone resins, petroleum resins, terpene resins, ketone resins, and water-insoluble resins such as coumarone resin.
Among these, as the water-soluble resin, polyvinyl alcohols, cellulose ethers and derivatives thereof, and starches are preferable, and polyvinyl alcohols are more preferable. The water-soluble resin can be used by dissolving in a solvent such as water.
Further, as the water-insoluble resin, styrene-butadiene resin, acrylic resin, and polyolefin resin are preferable, and styrene-butadiene resin is more preferable. The water-insoluble resin can be used as an emulsion dispersed in water or another medium in the form of an emulsification or paste.
Two or more kinds of these binders may be used in combination according to the required quality.

As the binder used in the undercoat layer of the present invention, it is preferable to use a water-soluble resin and a water-insoluble resin in combination at a certain ratio.
The weight ratio (solid content) of the water-soluble resin / water-insoluble resin is preferably 35/100 or less, more preferably 3/100 to 30/100, and still more preferably 5/100 to 25/100.
When the weight ratio of the water-soluble resin / water-insoluble resin exceeds 35/100, the heat discoloration resistance, print image quality, and head residue resistance tend to decrease.
Further, if the water-soluble resin is less than 3/100, the effect of suppressing migration described later cannot be sufficiently obtained, and the strength of the coating layer may be lowered.

Water-soluble resins such as polyvinyl alcohols generally have high viscosity and water retention and are easy to penetrate and fix in the voids of the undercoat layer containing the pigment having the specific shape and bulk density of the present invention. Therefore, it is considered that the gap in the undercoat layer is filled, and the heat discoloration resistance, the print image quality, and the head residue resistance are lowered.
On the other hand, water-insoluble resins such as styrene-butadiene resins generally have low viscosity and water retention, and pass through the undercoat layer containing a pigment having a specific shape and bulk density according to the present invention to the support. So-called migration that penetrates easily occurs.
By properly adjusting the mixing ratio of water-soluble resin and water-insoluble resin, the undercoat layer can be made bulky (low density) while suppressing migration. It is thought that the resistance to head scum can be obtained.

  In the present invention, in the range that does not inhibit the desired effect on the above problems, the undercoat layer is provided with a dispersant, a plasticizer, a thickener, a surfactant, a lubricant, a pH adjuster, an antifoaming agent, a water retention agent, an antiseptic, Various auxiliaries such as coloring dyes, ultraviolet absorbers, antioxidants, water and oil repellents can be used.

The amount of the pigment and binder used in the undercoat layer is determined according to the required performance and recordability and is not particularly limited. Usually, the pigment is used with respect to 100 parts by weight of the total solid content of the undercoat layer. The solid content is 50 to 95 parts by weight, preferably 70 to 90 parts by weight. The content of the binder is preferably 7 to 30 parts by weight, more preferably 10 to 25 parts by weight in terms of solid content.
The content of the cationic substance in the undercoat layer of the present invention is preferably 0.5 to 3.0 parts by weight in solid content with respect to 100 parts by weight of Rosetta type light calcium carbonate contained in the undercoat layer. This content is more preferably 0.5 to 2.5 parts by weight in terms of solid content because pigment aggregates are easily formed, and more preferably 1.0 to 2.0 parts by weight.
When organic hollow particles are further contained in the undercoat layer, the content of the organic hollow particles with respect to 100 parts by weight of the total solid content of the undercoat layer is preferably 1 to 18 parts by weight, more preferably 3 to 15 parts by weight. It is. Increasing the content of organic hollow particles tends to improve the color development sensitivity, but if the content exceeds 18 parts by weight, the residue adheres to the thermal head and the like, and the print running property (head residue resistance) decreases. There are things to do.

In the present invention, the support and the means for applying an undercoat layer on the support are not particularly limited, and are well known and commonly used on a support made of an appropriate material such as paper, recycled paper, plastic film, and synthetic paper. Can be applied according to technique. For example, an air machine, a rod blade coater, a vent blade coater, a bevel blade coater, a roll coater, a curtain coater, etc. When using a blade coater such as a blade coater, vent blade coater, or bevel blade coater, high-concentration coating is possible, so that the undercoat layer coating solution does not easily penetrate into the support and forms a uniform undercoat layer. Therefore, it is preferable.
The coating amount of the undercoat layer is determined according to the required performance and recording suitability, and is not particularly limited, but the general coating amount is about 1 to 15 g / m ² in terms of solid content, preferably 4 to 10 g / m ² .

  Next, various materials used in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention are exemplified, but a binder, a crosslinking agent, a pigment, and the like are provided as necessary as long as the desired effects on the above-described problems are not inhibited. It can also be used for each coating layer.

  As the developer, any known developer in the field of conventional pressure-sensitive or thermal recording paper can be used, and is not particularly limited. For example, activated clay, attapulgite, colloidal silica, aluminum silicate, etc. Inorganic acidic substance, 4,4′-isopropylidene diphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4′-dihydroxy Diphenyl sulfide, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 4,4′-dihydroxydiphenyl sulfone, 2,4′-dihydroxydiphenyl sulfone, 4-hydroxy-4′-isopropoxydiphenyl sulfone, 4-hydroxy-4 '-N-propoxydiphenylsulfone, bis (3 Allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4′-methyldiphenylsulfone, 4-hydroxyphenyl-4′-benzyloxyphenylsulfone, 3,4-dihydroxyphenyl-4′-methylphenylsulfone, 1- [ 4- (4-hydroxyphenylsulfonyl) phenoxy] -4- [4- (4-isopropoxyphenylsulfonyl) phenoxy] butane, a phenol condensation composition described in JP2003-154760, and JP8-59603A Aminobenzenesulfonamide derivatives, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, butyl bis (p-hydroxyphenyl) acetate, bis (p -Hydroxyphenyl) methyl acetate, 1 1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 1,3-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), 2,2′-thiobis (4-tert-octylphenol) ), Phenolic compounds such as diphenylsulfone cross-linking compounds described in WO 97/16420, compounds described in WO 02/081229 or JP-A 2002-301873, and N, N′-di-m-chlorophenylthiourea, etc. Thiourea compound, p-chlorobenzoic acid, stearyl gallate, bis [4- (n-octyloxycarbonylamino) ) Zinc salicylate] dihydrate, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- (p-tolylsulfonyl) propyloxy] salicylic acid, 5- [p- (2-p- Methoxyphenoxyethoxy) cumyl] aromatic carboxylic acids of salicylic acid, and salts of these aromatic carboxylic acids with polyvalent metal salts such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, and thiocyanic acid Examples include zinc antipyrine complexes and complex zinc salts of terephthalaldehyde acid with other aromatic carboxylic acids. These developers can be used alone or in combination of two or more. 1- [4- (4-Hydroxyphenylsulfonyl) phenoxy] -4- [4- (4-isopropoxyphenylsulfonyl) phenoxy] butane is available, for example, under the trade name JKY-214 manufactured by API Corporation. Yes, the phenol condensation composition described in JP-A No. 2003-154760 is available, for example, under the trade name JKY-224 manufactured by API Corporation, and is a diphenylsulfone cross-linking compound described in International Publication No. WO 97/16420 Is available under the trade name D-90 manufactured by Nippon Soda Co., Ltd. Moreover, the compound as described in WO02 / 081229 etc. is available as Nippon Soda Co., Ltd. brand name NKK-395 and D-100. In addition, a metal chelate color-developing component such as a higher fatty acid metal double salt and a polyvalent hydroxyaromatic compound described in JP-A-10-258577 can also be contained.

  As the leuco dye, those known in the conventional pressure-sensitive or thermal recording paper field can be used, and are not particularly limited. However, triphenylmethane compounds, fluorane compounds, fluorene compounds, divinyl compounds are not limited. Compounds and the like are preferred. Specific examples of typical colorless or light-colored dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination of two or more.

<Triphenylmethane leuco dye>
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide (also known as malachite green lactone)

<Fluoran leuco dye>
3-diethylamino-6-methylfluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-diethylamino- 6-methyl-7-chlorofluorane, 3-diethylamino-6-methyl-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7- (o-chloroanilino) fluorane, 3- Diethylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-diethylamino-6-methyl-7- (o-fluoroanilino) fluorane, 3-diethylamino-6-methyl-7- (m-methylanilino) fluorane 3-diethylamino-6-methyl-7-n-octylanilinofluorane, 3-di Tilamino-6-methyl-7-n-octylaminofluorane, 3-diethylamino-6-methyl-7-benzylaminofluorane, 3-diethylamino-6-methyl-7-dibenzylaminofluorane, 3-diethylamino- 6-chloro-7-methylfluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-diethylamino-6-chloro-7-p-methylanilinofluorane, 3-diethylamino-6-ethoxy Ethyl-7-anilinofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino- 7- (o-chloroanilino) fluorane, 3-diethylamino-7- (p Chloroanilino) fluorane, 3-diethylamino-7- (o-fluoroanilino) fluorane, 3-diethylamino-benzo [a] fluorane, 3-diethylamino-benzo [c] fluorane, 3-dibutylamino-6-methyl-fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-dibutylamino-6-methyl-7- ( o-chloroanilino) fluorane, 3-dibutylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-dibutylamino-6-methyl-7- (o-fluoroanilino) fluorane, 3-dibutylamino-6 -Methyl-7- (m-trifluoromethylanilino) fluorane, 3-dibutylamino- 6-methyl-7-chlorofluorane, 3-dibutylamino-6-ethoxyethyl-7-anilinofluorane, 3-dibutylamino-6-chloro-7-anilinofluorane, 3-dibutylamino-6- Methyl-7-p-methylanilinofluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-dibutylamino-7- (o-fluoroanilino) fluorane, 3-di-n-pentylamino -6-methyl-7-anilinofluorane, 3-di-n-pentylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-di-n-pentylamino-7- (m-trifluoro Methylanilino) fluorane, 3-di-n-pentylamino-6-chloro-7-anilinofluorane, 3-di-n-pentylamino-7- (p-chloro) Nilino) fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-propylamino) -6-methyl -7-anilinofluorane, 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-cyclohexylamino) -6-methyl-7 -Anilinofluorane, 3- (N-ethyl-N-xylamino) -6-methyl-7- (p-chloroanilino) fluorane, 3- (N-ethyl-p-toludino) -6-methyl-7-ani Linofluorane, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-chloro-7-a Linofluorane, 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isobutylamino) -6-methyl-7-anilinofur Oran, 3- (N-ethyl-N-ethoxypropylamino) -6-methyl-7-anilinofluorane, 3-cyclohexylamino-6-chlorofluorane, 2- (4-oxahexyl) -3-dimethyl Amino-6-methyl-7-anilinofluorane, 2- (4-oxahexyl) -3-diethylamino-6-methyl-7-anilinofluorane, 2- (4-oxahexyl) -3-dipropyl Amino-6-methyl-7-anilinofluorane, 2-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane, 2-methoxy-6-p -(P-dimethylaminophenyl) aminoanilinofluorane, 2-chloro-3-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane, 2-chloro-6-p- (p- Dimethylaminophenyl) aminoanilinofluorane, 2-nitro-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-amino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-phenyl-6-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane, 2-benzyl-6 -P- (p-phenylaminophenyl) aminoanilinofluorane, 2-hydroxy-6-p- (p-phenylamino) Nophenyl) aminoanilinofluorane, 3-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane, 3-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 3 -Diethylamino-6-p- (p-dibutylaminophenyl) aminoanilinofluorane, 2,4-dimethyl-6-[(4-dimethylamino) anilino] -fluorane

<Fluorene leuco dye>
3,6,6′-tris (dimethylamino) spiro [fluorene-9,3′-phthalide], 3,6,6′-tris (diethylamino) spiro [fluorene-9,3′-phthalide]

<Divinyl leuco dye>
3,3-bis- [2- (p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [2- (P-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalide, 3,3-bis- [1,1-bis (4-pyrrolidinophenyl) ) Ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2- Yl] -4,5,6,7-tetrachlorophthalide

<Others>
3- (4-Diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- ( 1-octyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-cyclohexylethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl)- 4-azaphthalide, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, 3,6-bis (diethylamino) fluorane-γ- (3′-nitro) anilinolactam, 3,6 -Bis (diethylamino) fluorane-γ- (4′-nitro) anilinolactam, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylamino) Enyl) -ethenyl] -2,2-dinitrileethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2- β-naphthoylethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2,2-diacetylethane, bis- [2, 2,2 ′, 2′-Tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

  A conventionally well-known sensitizer can be used as a sensitizer. Examples of the sensitizer include fatty acid amides such as stearamide and palmitic acid amide, ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-bis- (3-methylphenoxy) ethane, p-benzylbiphenyl, β- Benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, dibenzyl oxalate, di (p-chlorobenzyl) oxalate, di (p-methylbenzyl) oxalate, Dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, o-xylene-bis -(Phenyl ether), 4- (m-me Tilphenoxymethyl) biphenyl, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di (3-methylphenoxy) ethylene, bis [2- (4-methoxy- Phenoxy) ethyl] ether, methyl p-nitrobenzoate, phenyl p-toluenesulfonate, o-toluenesulfonamide, p-toluenesulfonamide and the like. These sensitizers may be used alone or in combination of two or more.

  Examples of the pigment include kaolin, calcined kaolin, calcium carbonate, aluminum oxide, titanium oxide, magnesium carbonate, aluminum silicate, magnesium silicate, calcium silicate, aluminum hydroxide, silica and the like, and can be used in combination according to the required quality. .

  As the binder, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetyl modified polyvinyl alcohol, carboxy modified polyvinyl alcohol, amide modified polyvinyl alcohol, sulfonic acid modified polyvinyl alcohol, butyral modified polyvinyl alcohol, olefin modified polyvinyl alcohol, Nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer and ethyl cellulose, acetyl Cellulose derivatives such as cellulose Casein, arabic gum, oxidized starch, etherified starch, dialdehyde starch, esterified starch, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic ester, polyvinyl butyral, polystyrose and copolymers thereof, polyamide resin, Silicone resin, petroleum resin, terpene resin, ketone resin, coumarone resin and the like can be exemplified. These polymer substances are used by dissolving them in solvents such as water, alcohol, ketones, esters, hydrocarbons, etc., and are used in the state of being emulsified or pasted in water or other media to achieve the required quality. It can also be used in combination.

  As the crosslinking agent, polyamine / polyamide resins such as polyamide urea resin, polyalkylene polyamine resin, polyalkylene polyamide resin, polyamine polyurea resin, polyalkylene polyamine urea formalin resin, or polyalkylene polyamine polyamide polyurea resin, glyoxal And methylol melamine, melamine formaldehyde resin, melamine urea resin, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, ammonium chloride and the like.

  Examples of the lubricant include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, and silicone resins.

  In the present invention, 4,4′-butylidene (6-tert-butyl-3-methylphenol), 2 as a stabilizer for improving the oil resistance and the like of the image area as long as the desired effect on the above problems is not impaired. 2,2'-di-t-butyl-5,5'-dimethyl-4,4'-sulfonyldiphenol, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane and the like can also be added. In addition, benzophenone and triazole ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, and the like can be used.

  The types and amounts of the leuco dye, developer, sensitizer, and other various components used in the heat-sensitive recording layer of the present invention are determined according to the required performance and recording suitability, and are not particularly limited. Usually, 0.5 to 10 parts by weight of developer, 0.1 to 10 parts by weight of sensitizer, 0.5 to 20 parts by weight of pigment, and 0.01 to 10 parts by weight of stabilizer for 1 part by weight of leuco dye. Parts and other components of about 0.01 to 10 parts by weight. The binder is suitably about 5 to 25% by weight based on the solid content of the heat-sensitive recording layer.

  In the present invention, the leuco dye, the developer, and the material to be added as necessary are finely divided to a particle size of several microns or less by a pulverizer such as a ball mill, an attritor, or a sand glider, or an appropriate emulsifying device, and a binder. Depending on the purpose, various additive materials are added to obtain a coating solution. As a solvent used for this coating liquid, water or alcohol can be used, and its solid content is about 20 to 40% by weight.

  The heat-sensitive recording material of the present invention has an undercoat layer on the support and a heat-sensitive recording layer provided on the undercoat layer, but a layer other than the undercoat layer and the heat-sensitive recording layer may be provided as appropriate. For example, a protective layer can be provided on the heat-sensitive recording layer, and a backcoat layer can be provided on the opposite side of the support from the heat-sensitive recording layer.

In the present invention, means for applying a coating layer other than the undercoat layer, that is, a heat-sensitive recording layer, a protective layer, a backcoat layer, and the like are not particularly limited, and can be applied according to a well-known common technique. For example, an off-machine coating machine or an on-machine coating machine equipped with various coaters such as an air knife coater, a rod blade coater, a vent blade coater, a bevel blade coater, a roll coater, and a curtain coater is appropriately selected and used.
The coating amount of the coating layer other than the undercoat layer is determined according to the required performance and recording suitability, and is not particularly limited, but the general coating amount of the heat-sensitive recording layer is 2.0% in terms of solid content. a ~12.0g / ^{m 2} approximately, the coating amount of the protective layer is 0.5 to 5.0 g / ^{m 2} is preferred solids.
Further, various known techniques in the heat-sensitive recording material field can be added as appropriate, such as applying a smoothing process such as supercalendering after coating each coating layer.

  The following examples illustrate the invention but are not intended to limit the invention. In Examples and Comparative Examples, “parts” represents “parts by weight” and “%” represents “% by weight” unless otherwise specified. Various dispersions or coating solutions were prepared as follows.

[Reference Example 1]
A composition comprising the following composition was stirred and dispersed to prepare an undercoat layer coating solution.
<Undercoat layer coating solution 1>
Rosetta type light calcium carbonate (Specialty Minerals
Inc. (Product name: Albuquerque LO, bulk density: 210 g / L)
100.0 parts Styrene-butadiene copolymer latex (manufactured by Zeon Corporation, trade name:
ST5526, solid content 48%) 40.0 parts Completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., Ltd., trade name: PVA)
117, solid content 10%) 30.0 parts water 100.0 parts

Next, the undercoat layer coating solution 1 was applied to one side of a support (high-quality paper having a basis weight of 60 g / m ² ) with a vent blade coater so that the coating amount was 10.0 g / m ² in terms of solid content. Thereafter, drying was performed to obtain an undercoat layer-coated paper.

The developer dispersion (liquid A) and the leuco dye dispersion (liquid B) having the following composition were separately wet-ground with a sand grinder until the average particle size became 0.5 μm.
Developer dispersion (liquid A)
4-hydroxy-4'-isopropoxydiphenylsulfone (manufactured by API Corporation, trade name: NYDS) 6.0 parts fully saponified polyvinyl alcohol aqueous solution (trade name: PVA, manufactured by Kuraray Co., Ltd.)
117, solid content 10%) 18.8 parts water 11.2 parts
Leuco dye dispersion (liquid B)
3-dibutylamino-6-methyl-7-anilinofluorane (manufactured by Yamamoto Kasei Co., Ltd., trade name: ODB-2) 6.0 parts complete saponified polyvinyl alcohol aqueous solution (Kuraray Co., Ltd., trade name: PVA)
117, solid content 10%) 4.6 parts water 2.6 parts

Subsequently, each dispersion liquid was mixed in the following ratio to prepare a thermosensitive recording layer coating liquid.
<Thermosensitive recording layer coating solution 1>
Developer dispersion (liquid A) 36.0 parts Leuco dye dispersion (liquid B) 13.2 parts Completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., Ltd., trade name: PVA)
117, solid content 10%) 25.0 parts Aluminum hydroxide (made by Showa Denko KK, trade name: Heidilite H-32,
50% dispersion) 12.0 parts

Next, on the undercoat layer of the undercoat layer-coated paper, the thermal recording layer coating solution 1 is applied with a rod blade coater so that the coating amount is 2.5 g / m ^{2 in} solid content, and then dried. And a heat-sensitive recording material was obtained by processing with a super calendar so that the smoothness was 500 to 1000 seconds.

[Example 1]
In the undercoat layer coating solution 1, a cationic sizing agent (trade name: SE2250, manufactured by Seiko PMC, trade name: 35%, hereinafter referred to as “cationic sizing agent A”) with respect to 100 parts of Rosetta-type light calcium carbonate. Was added in the same manner as in Reference Example 1 except that 0.6 part (0.2 parts in terms of solid content) was added.
[Example 2]
In the same manner as in Reference Example 1, except that 2.9 parts of cationic sizing agent A (1.0 part in terms of solid content) was added to 100 parts of Rosetta-type light calcium carbonate in undercoat layer coating liquid 1. Thus, a heat-sensitive recording material was produced.
[Example 3]
In the same manner as in Reference Example 1, except that 4.3 parts of cationic sizing agent A (1.5 parts in terms of solid content) was added to 100 parts of Rosetta-type light calcium carbonate in undercoat layer coating liquid 1. Thus, a heat-sensitive recording material was produced.
[Example 4]
In the same manner as in Reference Example 1, except that 7.1 parts of cationic sizing agent A (2.5 parts in terms of solid content) was added to 100 parts of Rosetta-type light calcium carbonate in undercoat layer coating liquid 1. Thus, a heat-sensitive recording material was produced.
[Example 5]
In the undercoat layer coating liquid 1, a cationic sizing agent (trade name: SS2753, manufactured by Seiko PMC Co., Ltd., solid content 20%, hereinafter referred to as “cationic sizing agent B”) with respect to 100 parts of Rosetta type light calcium carbonate. Was added in the same manner as in Reference Example 1 except that 7.5 parts (1.5 parts in terms of solid content) was added.

[Example 6]
In the undercoat layer coating liquid 1, 7.5 parts of cationized starch aqueous solution (Abebe Japan Co., Ltd., trade name: Amylofax T2600, solid content 20%) with respect to 100 parts of Rosetta type light calcium carbonate (in terms of solid content) A heat-sensitive recording material was produced in the same manner as in Reference Example 1 except that 1.5 parts) was added.
[Example 7]
Reference Example 1 except that 30.0 parts of magnesium sulfate aqueous solution (5% solid content) (1.5 parts in terms of solid content) was added to 100 parts of Rosetta-type light calcium carbonate to the undercoat layer coating solution 1. A thermosensitive recording material was produced in the same manner as described above.

[Reference Example 2]
Other than using Rosetta-type light calcium carbonate (product of Specialty Minerals Inc., trade name: Albuquer 5970, bulk density: 250 g / L) instead of rosetta-type light calcium carbonate (Albuquer LO) in undercoat layer coating solution 1 Produced a heat-sensitive recording material in the same manner as in Reference Example 1.
[Reference Example 3]
A heat-sensitive recording material was used in the same manner as in Reference Example 1 except that calcined clay (trade name: Ansilex 93) manufactured by BASF was used in place of the Rosetta-type light calcium carbonate (Albuquer LO) in the undercoat layer coating solution 1. Was made.

[Reference Example 4]
0.8 parts of polyamide epichlorohydrin resin (manufactured by Seiko PMC, trade name: WS4030, solid content 25%) with respect to 100 parts of rosetta type light calcium carbonate in the undercoat layer coating liquid 1 (in terms of solid content) 0.2 part) A heat-sensitive recording material was produced in the same manner as in Reference Example 1 except that it was added.
[Reference Example 5]
Reference Example 1 except that 4.0 parts (1.0 part in terms of solid content) of polyamide epichlorohydrin resin (WS4030) was added to the undercoat layer coating liquid 1 with respect to 100 parts of Rosetta-type light calcium carbonate. A thermosensitive recording material was produced in the same manner as described above.
[Reference Example 6]
Reference Example 1 except that 6.0 parts of polyamide epichlorohydrin resin (WS4030) was added to 100 parts of Rosetta-type light calcium carbonate to the undercoat layer coating solution 1 (1.5 parts in terms of solid content). A thermosensitive recording material was produced in the same manner as described above.

[Reference Example 7]
Reference Example 1 except that 10.0 parts of polyamide epichlorohydrin resin (WS4030) was added to 2.5 parts of rosetta type light calcium carbonate to the undercoat layer coating liquid 1 (2.5 parts in terms of solid content) A thermosensitive recording material was produced in the same manner as described above.
[Reference Example 8]
In the undercoat layer coating liquid 1, 7.5 parts (in terms of solid content) of polyamine epichlorohydrin resin (manufactured by Seiko PMC, trade name: WS4010, solid content 20%) with respect to 100 parts of rosetta type light calcium carbonate A heat-sensitive recording material was produced in the same manner as in Reference Example 1 except that 1.5 parts) was added.
[Reference Example 9]
12.5 parts of cationic polyacrylamide (trade name: DH4196, solid content 12%) manufactured by Seiko PMC Co., Ltd. with respect to 100 parts of Rosetta-type light calcium carbonate in the undercoat layer coating solution 1 (in terms of solid content). 5 parts) A heat-sensitive recording material was produced in the same manner as in Reference Example 1 except that it was added.

The following evaluation was performed about the produced thermosensitive recording material.
<Color development sensitivity (print density)>
Using the TH-PMD manufactured by Okura Electric Co., Ltd. (with a thermal recording paper printing tester and a Kyocera thermal head), the produced thermal recording medium was solid printed at an applied energy of 0.27 mJ / dot and a printing speed of 50 mm / sec. did. The printing density of the solid printing part was measured with a Macbeth densitometer (RD-914, using an amber filter) to evaluate the color development sensitivity.

<Heat-resistant discoloration of blank paper>
The produced thermal recording material was treated in an environment of 80 ° C. for 1 hour and then allowed to stand in an environment of 23 ° C. and 50% RH for 3 hours.
Measure the density of the non-printing area (blank area) with a Macbeth densitometer (RD-914, using amber filter), calculate the ground color value from the difference between the values before and after processing, and heat resistance of the non-printing area (blank area) Sex was evaluated according to the following criteria. If the evaluation is good or acceptable, there is no practical problem.
Ground color development value = (density of non-printed part after processing)-(density of non-printed part before processing)
Good: Ground color development value is less than 0.3 Possible: Ground color development value is 0.3 or more and less than 0.4 Impossibility: Ground color development value is 0.4 or more

<Print quality>
Using the TH-PMD manufactured by Okura Electric Co., Ltd. (with a thermal recording paper printing tester and a Kyocera thermal head installed), the printed thermal recording medium was solid printed at an applied energy of 0.15 mJ / dot and a printing speed of 50 mm / sec. did. The solid print portion was visually observed, and the print image quality was evaluated according to the following criteria. If the evaluation is excellent, good, or acceptable, there is no practical problem.
Excellent: No white spots are observed.
Good: Some white spots are observed, but the whole is solid.
Good: A white portion is observed, but the whole is generally solid.
Impossible: There are many white areas.

<Printability (head residue resistance)>
The produced thermal recording material was solid-printed with an applied energy of 0.20 mJ / dot under an environment of −10 ° C. using a printing tester (manufactured by Canon Inc., HT180). The state of the thermal head deposit after 1 m printing was visually observed and evaluated according to the following criteria. If the evaluation is excellent, good, or acceptable, there is no practical problem.
Excellent: No deposits.
Good: Almost no deposits.
Yes: There are some deposits.
Impossible: There are many deposits.

<Surface strength>
About the produced thermosensitive recording material, 1.0 cc of printing ink (Toyo Ink Manufacturing Co., Ltd., PRINTING INK, black ink, SMX, Tack 15) is used with an RI printing machine (Meiji Seisakusho, RI-3 type printing machine). Printing was performed on the thermal recording surface. The degree of picking with ink (peeling of the heat-sensitive recording layer and the support) was visually observed and evaluated according to the following criteria. If the evaluation is excellent, good, or acceptable, there is no practical problem.
Excellent: No heat-sensitive recording layer or support is peeled off.
Good: Slight peeling of the heat-sensitive recording layer is observed.
Good: Peeling of the heat-sensitive recording layer is scattered, but peeling of the support is not seen.
Impossible: The heat-sensitive recording layer is peeled off frequently or the support is peeled off.

<Reprintability> (Color sensitivity after storage)
The produced thermal recording material was stored for 24 hours in an environment of 40 ° C. and 90% RH. A TH-PMD manufactured by Okura Electric Co., Ltd. (with a thermal recording paper printing tester and a Kyocera thermal head installed) was used as the thermal recording medium after storage, and the solid was applied at an applied energy of 0.27 mJ / dot and a printing speed of 50 mm / sec. Printed. The printing density of the solid printing part was measured with a Macbeth densitometer (RD-914, using an amber filter), and the coloring sensitivity after storage was evaluated.

The evaluation results are shown in Table 1.

Claims (8)

A support, an undercoat layer containing a pigment and a binder as main components provided on the support, and further containing a cationic substance, and a colorless or light-colored electron donating property provided on the undercoat layer A thermosensitive recording medium comprising a thermosensitive recording layer containing a leuco dye and an electron-accepting developer as main components, wherein the pigment contained in the undercoat layer is formed by agglomerating spindle-shaped primary particles radially. A heat-sensitive recording material, which is rosetta-type light calcium carbonate formed by forming secondary particles, and has a bulk density of 240 g / L or less. The heat-sensitive recording material according to claim 1, wherein the cationic substance is at least one selected from the group consisting of a cationic sizing agent, a cationized starch, and a water-soluble metal salt. The heat-sensitive recording material according to claim 2, wherein the cationic substance is a cationic sizing agent, and the cationic sizing agent is a styrene sizing agent or a styrene acrylate sizing agent. The binder contained in the undercoat layer comprises a water-soluble resin and a water-insoluble resin, and the weight ratio of water-soluble resin / water-insoluble resin is 35/100 or less. Thermal recording material. The heat-sensitive recording material according to claim 4, wherein the water-soluble resin is a polyvinyl alcohol. The heat-sensitive recording material according to claim 4 or 5, wherein the water-insoluble resin is a styrene-butadiene resin. The heat-sensitive recording material according to claim 1, wherein the rosetta-type light calcium carbonate is 70% by weight or more of the total pigment contained in the undercoat layer. The thermosensitive recording material according to any one of claims 1 to 7, wherein the content of the cationic substance in the undercoat layer is 0.5 to 3.0 parts by weight with respect to 100 parts by weight of Rosetta type light calcium carbonate. .